onnxruntime

Fix usage of enable_training_ops and reduce ifdef complexity for training builds (#13888)

### Description
Fix usage of enable_training_ops and reduce ifdef complexity for
training builds.




### Motivation and Context
This is the second refactoring PR towards creating a dedicated build for
on device training. This PR aims to reduce some complexity. We can set
ENABLE_TRAINING_OPS in cmake when either ENABLE_TRAINING or
ENABLE_TRAINING_ON_DEVICE is selected, this way we dont have to use if
defined(ENABLE_TRAINING) || defined(ENABLE_TRAINING_ON_DEVICE )
everywhere in the code.

- If it fixes an open issue, please link to the issue here. -->